1. Field of the Invention
This invention relates to improvements in a torch ignition type internal combustion engine which has no intake valve in the auxiliary combustion chamber.
It is well known in the art that to burn a rather lean air-fuel mixture in an engine cylinder is quite effective to reduce the toxic components such as carbon monoxide, unburned hydrocarbons and nitrogen oxides which are usually present in the exhaust gas. A lean air-fuel mixture, however, has potentially inferior ingnitability and low flame propagation velocity, compared to those of rich mixture, therefore it is crucially important for an engine which burns a lean air-fuel mixture to stabilize the ignitability and to increase its flame propagation velocity, otherwise poor thermal efficiency and/or toxic exhaust gas would result.
2. Description of Prior Art
In order to overcome the aforementioned difficulties, there has been introduced the so-called torch ignition type internal combustion engine which has a main combustion chamber with an intake valve and an exhaust valve, and an auxiliary combustion chamber with an auxiliary intake valve, the engine being adapted to supply a lean air-fuel mixture to the main combustion chamber and a relatively rich mixture to the auxiliary combustion chamber through the respective intake valves. In such an engine system, the relatively rich air-fuel mixture in the auxiliary combustion chamber is first ignited and burned, the flame bursting out from the auxiliary combustion chamber successively ignites the lean air-fuel mixture in the main combustion chamber. This internal combustion engine with an auxiliary intake valve in the auxiliary chamber has its own merit and demerit, that is, it improves the ignitability since a rich air-fuel mixture is initially ignited by a spark plug and the high flame propagation velocity is resulted by the strong torch flame. On the other hand, such internal combustion engine inevitably requires extra parts such as an auxiliary intake valve in the auxiliary combustion chamber and the complicated mechanism for operating the auxiliary valve.
The present inventors have previously proposed a torch ignition type internal combustion engine which comprises a main combustion chamber with an intake valve and an exhaust valve, an auxiliary combustion chamber with no intake valve, a passage interconnecting the main and auxiliary combustion chambers, and an ignition plug having its sparking electrodes located in a position contiguous to the interconnecting passage. In this torch ignition type internal combustion engine, a lean air-fuel mixture sucked into the main combustion chamber through the intake valve during the intake stroke of the piston is pushed into the auxiliary combustion chamber during the succeeding compression stroke through the passage interconnecting the main and auxiliary combustion chambers. In this engine, a relatively lean air-fuel mixture can be ignited since there is only fresh air-fuel mixture around the sparking electrode of the ignition plug, that is, there is no residual gas remaining around the electrode at the time of ignition, because the residual gas in the above mentioned passage has been flown into the auxiliary combustion chamber by fresh mixture during compression stroke.
In the above-described torch ignition type internal combustion engine with no intake valve in the auxiliary combustion chamber, it is however, more desirable to have richer air-fuel mixture around the sparking electrodes of the ignition plug in order to have more ensured ignitability under any operating conditions of the engine.